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Call processing system and method based on answer mode of push to talk
over cellular user

Abstract

A call processing system and method based on an answer mode of a
Push-to-Talk over Cellular (PoC) user are provided. A data format is
defined, which inserts an indicator indicating a manual answer override
into a payload of a Real-time Transport Control Protocol (RTCP) in a
format of a new data field. When a PoC communication requester instructs
the MAO to perform PoC communication regardless of an answer mode of a
reception side PoC user, an auto-answer mode is immediately executed
without any procedure of checking the instruction. In addition, when the
reception side PoC user establishes an early session with a home PoC
server in its own PoC terminal, the call processing can be performed at a
quicker speed.

1. A call processing system based on a manual answer override (MAO) in a
Push-to-Talk over Cellular (PoC) network, the call processing system
comprising: a transmission side PoC system having a transmission side PoC
client and a transmission side PoC server for sending a PoC communication
request message to a reception side PoC server, the PoC communication
request message including an MAO indication; and a reception side PoC
system having the reception side PoC server for recognizing the MAO
indication included in the PoC communication request message received
from the transmission side PoC server and sending a response message to
the transmission side PoC system in response to the PoC communication
request message, and a reception side PoC client for receiving a talk
burst signal including the MAO indication from the reception side PoC
server.

2. The call processing system according to claim 1, wherein the MAO
indication is included in the talk burst signal by any one of the
transmission side PoC client, the transmission side PoC server and the
reception side PoC server.

3. The call processing system according to claim 1, wherein the talk burst
signal is implemented in a payload format of a Real-time Transport
Control Protocol (RTCP) packet.

4. The call processing system according to claim 3, wherein the payload
format of the RTCP packet includes a version information field, a subtype
information field, a length field, a general transmission related
information field, a PoC user address field, a name information field and
an MAO indication information field.

5. The call processing system according to claim 1, wherein the reception
side PoC server sends the response message to the transmission side PoC
system without sending the PoC communication request message to the
reception side PoC client.

6. The call processing system according to claim 1, wherein the talk burst
signal is sent from the transmission side PoC system to the reception
side PoC server.

7. A call processing method based on a manual answer override (MAO) in a
Push-to-Talk over Cellular (PoC) network, the call processing method
comprising the steps of: sending a PoC communication request message
including an MAO indication from a transmission side PoC server to a
reception side PoC server; recognizing, by the reception side PoC server,
the MAO indication included in the PoC communication request message and
sending a response message to the transmission side PoC server in
response to the PoC communication request message; and receiving, by a
reception side PoC client, a talk burst signal including the MAO
indication from the reception side PoC server.

8. The call processing method according to claim 7, wherein the MAO
indication is included in the talk burst signal by any one of the
transmission side PoC client, the transmission side PoC server and the
reception side PoC server.

9. The call processing method according to claim 7, wherein the reception
side PoC server sends the response message to the transmission side PoC
system without sending the PoC communication request message to the
reception side PoC client.

10. The call processing method according to claim 7, wherein the talk
burst signal is implemented in a payload format of a Real-time Transport
Control Protocol (RTCP) packet.

11. The call processing method according to claim 10, wherein the payload
format of the RTCP packet includes a version information field, a subtype
information field, a length field, a general transmission related
information field, a PoC user address field, a name information field and
an MAO indication information field.

12. The call processing method according to claim 7, wherein the talk
burst signal is sent from the transmission side PoC system to the
reception side PoC server.

13. A method for performing a manual answer override (MAO) in a
Push-to-Talk over Cellular (PoC) network, the method comprising steps of:
receiving a talk burst signal including an MAO indication from a PoC
server; and detecting the MAO indication included in the talk burst
signal, the MAO indication being a first MAO information sent from the
PoC server to a PoC client.

14. The method according to claim 13, wherein the talk burst signal is
implemented in a payload format of a Real-time Transport Control Protocol
(RTCP) packet.

15. The method according to claim 14, wherein the RTCP packet includes a
version information field, a subtype information field, a length field, a
general transmission related information field, a PoC user address field,
a name information field and an MAO indication information field.

16. The method according to claim 13, further comprising the step of
informing a user of the PoC client that a PoC communication is requested
by another user authorized to use the MAO according to the detection of
the MAO indication.

17. The method according to claim 16, wherein the informing step includes
a displaying information relating to a PoC communication requester.

18. The method according to claim 17, wherein the information relating to
the PoC communication requester includes a name of the PoC communication
requester.

19. The method according to claim 17, wherein the information relating to
the PoC communication requester includes a PoC address of the PoC
communication requester.

20. A Push-to-Talk over Cellular (PoC) client for performing a manual
answer override (MAO) in a PoC network, comprising means for receiving a
talk burst signal including an MAO indication from a PoC server and
detecting the MAO indication included in the talk burst signal, wherein
the MAO indication is a first MAO information sent from the PoC server to
the PoC client.

21. The PoC client according to claim 20, wherein the talk burst signal is
implemented in a payload format of a Real-time Transport Control Protocol
(RTCP) packet.

22. The PoC client according to claim 21, wherein the RTCP packet includes
a version information field, a subtype information field, a length field,
a general transmission related information field, a PoC user address
field, a name information field and an MAO indication information field.

23. The PoC client according to claim 20, wherein the PoC client informs a
user of the PoC client that a PoC communication is requested from another
user authorized to make use of the MAO according to the detection of the
MAO indication.

24. The PoC client according to claim 23, wherein the PoC client informs
the user by displaying information relating to a PoC communication
requester.

25. The PoC client according to claim 24, wherein the information relating
to the PoC communication requester includes a name of the PoC
communication requester.

26. The PoC client according to claim 24, wherein the information relating
to the PoC communication requester includes a PoC address of the PoC
communication requester.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. .sctn.119 to an
application entitled "Call Processing System and Method Based On Answer
Mode of Push to Talk Over Cellular User," filed in the Korean
Intellectual Property Office on Sep. 24, 2004 and assigned Serial No.
2004-77172, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a call processing system
and method based on an answer mode of a PoC (Push-to-Talk over Cellular)
user.

[0006] Currently, PTT services include various additional functions such
as an instant messenger function, a status indication function, etc., in
addition to existing voice communication functions which are provided by
radio sets, TRSs (Trunked Radio Systems), etc.

[0007] Currently, efforts are being made to enact a standard for a PTT
over Cellular (PoC) service using a mobile communication network. The PoC
service has various features which distinguish it from existing mobile
communication services. For example, an OMA (Open Mobile Alliance), a
group that defines specifications designed for mobile communication
services, has set forth standards which specify that a user of a mobile
communication device should be allowed to make a call while moving
between a plurality of sessions.

[0008] Hereinafter, a structure of a general PoC service system will be
described.

[0009] A block diagram illustrating a general PoC architecture is shown in
FIG. 1. A PoC client 10 is a service requester that is mounted in a
mobile phone, and is usually connected with a SIP/IP (Session Initiation
Protocol/Internet Protocol) core 30 via an access network 20, wherein the
SIP/IP core is a core element for supporting both SIP and IP multimedia.

[0010] Here, the PoC client 10 provides access to a PoC service while
residing in a PoC user terminal. The PoC client's 10 main functions are
establishing a PoC session, participating in an existing PoC session, and
terminating the established PoC session. In addition, the PoC client 10
performs other functions such as creating and sending a talk burst,
supporting an instant personal alert, performing authentication on
obtaining access to the PoC service, and so forth. Hereinafter, unless
otherwise indicated, the term "PoC client 10" refers to a PoC service
subscriber.

[0011] The SIP/IP core is connected with a PoC server 60, a GLMS (Group
List Management System) 50 and a presence server 70 in order to support
the PoC service, thereby providing the PoC service.

[0012] Here, the PoC server 60 may perform a Controlling PoC Function (CF)
for maintaining and managing the PoC session, a Participating PoC
Function (PF) for participating in the PoC session which is established
for a one-to-one communication or a many-to-many communication, and so
forth.

[0013] To be specific, the CF maintains and manages the PoC sessions, and
the PF takes charge of maintenance and management of each PoC session.
Moreover, although the CF and the PF are different functions which are
performed by the PoC server, the PoC server may perform the CF and the PF
at the same time. The CF and the PF will be described in more detail with
reference to Table 1 and Table 2.
TABLE-US-00001
TABLE 1
Controlling PoC Function (CF)
Provides centralized PoC session handling
Provides the centralized Media distribution
Provides the centralized Talk Burst Arbitration functionality
including talker identification
Provides SIP session handling, such as SIP session origination,
termination, etc.
Provides policy enforcement for participation in group sessions
Provides the participants' information
Collects and provides centralized media quality information
Provides centralized charging reports
May provide transcoding between different codecs
Support Talk Burst Control Protocol Negotiation

[0014] As illustrated in Table 1, the CF manages PoC sessions on the
whole, particularly to receive, sequence and authorize right-to-speak
(i.e., a floor) requests of the PoC clients, to distribute a talk burst
requested by an arbitrary PoC client to all the other PoC clients
participating in a group calling, and to provide information about the
PoC clients participating in the group calling.

[0015] As in Table 2, the PF serves to manage the PoC session connected
with the CF and each PoC client, particularly, to relay a floor when the
PoC client requests the floor or when the CF assigns the floor to the PoC
client. Further, the PF serves; (1) to relay media between the CF and the
PoC client; (2) to perform transcoding when different codecs are used
between the CF and the PoC client; and (3) when two simultaneous sessions
are established, for example when a PoC user is invited to the other
session while participating in one session, to filter any one of the
sessions according to selection of the PoC user.
TABLE-US-00002
TABLE 2
Participating PoC Function (PF)
Provides PoC session handling
May provide the media relay function between PoC Client and
Controlling PoC server
May provide user media adaptation procedures
May provide the Talk Burst control message relay function between
PoC Client and Controlling PoC server
Provides SIP session handling, such as SIP session origination,
termination, etc, on behalf of the represented PoC Client.
Provides policy enforcement for incoming PoC session (e.g. access
control, incoming PoC session barring, availability status, etc)
May collect and provide media quality information
Provides the participant charging reports
May provide filtering of the media streams in the case of
simultaneous sessions
May provide transcoding between different codecs
May support Talk Burst Control Protocol Negotiation
Stores the current Answer Mode and Incoming PoC Session Barring
preferences of the PoC Client

[0016] In the PoC system configured as mentioned above, a certain PoC user
can input information on groups of other PoC users and their members into
the GLMS 50 by means of the terminal of the PoC user, or can ascertain
information about the other PoC users who can be called out through an
individual or group list received from the GLMS 50. Moreover, another
method capable of generating, correcting and managing the groups and
their members at the GLMS can input such information through a
communication network, such as the Internet, an intranet or so forth.

[0017] In order to make use of a PoC calling service, the PoC user
registers his/her PoC address with the SIP/IP. At this time, the SIP/IP
core stores information on the PoC user on the basis of a request of the
PoC user. Therefore, when another PoC user attempts a PoC group calling,
the other PoC user registers its own information with the SIP/IP core in
advance as set forth above, and provides a request for the calling to the
SIP/IP core by using the group identification information received from
the GLMS. Here, the SIP/IP core goes through the processes of determining
the address and positioning a domain by using the information about the
requesting PoC user, and then sends a request for PoC communication to a
home PoC server with which the requesting PoC user is registered. The PoC
server prepares an opening of the PoC session with regard to the PoC
communication request, obtains information about each PoC user from a
GLMS server, and sends a communication request signal to the
corresponding SIP/IP core. At this time, in the case of the communication
request of the users within an intra-domain, the PoC server performs the
PF and the CF. The PoC server managing the PoC user provided with the
communication request goes through the process of locating the SIP/IP
core by using the information about the PoC user which is sent to the PoC
server, and then makes the communication request to the PoC user.

[0018] Hereinafter, the call processing for a PoC communication setup will
be described according a reception-side viewpoint and a transmission-side
viewpoint. Features of the PoC system which are required according to the
OMA for each of the reception and transmission side setups are as
follows. First, an answer mode can be set according to a request of the
PoC user. The answer mode can be generally divided into an auto-answer
mode and a manual answer mode.

[0019] In the auto-answer mode, when a certain sender is included in a
list of the PoC users designated to make an auto-answer on the reception
side, an auto-answer is immediately sent to the transmission side in the
network instead of a manual answer of a receiver.

[0020] Meanwhile, the manual answer mode is applied when the sender is not
included in the list of PoC users for the auto-answer, when the sender is
not known or when the receiver is set to manually answer all the PoC
users, which means that a PoC communication request is sent to a user's
terminal via a receiving network, and thereby the communication is
connected by permission of the PoC user. Here, each of the answer modes
and list information are set and stored in the PoC server belonging to a
home network of each of the respective PoC users.

[0021] Second, the PoC system is divided into an on-demand session mode
and a pre-established session mode according to whether the PoC client is
connected with a PoC server within the home network of the PoC user.

[0022] The pre-established session mode means that the PoC user
establishes a specific session in advance (i.e., establishes an early
session) between the PoC client and the PoC server belonging to the
user's home network at the request of the user. This pre-established
session is required for a fast communication setup. To this end, the PoC
user previously negotiates with the PoC server to define server-client
media parameters that the PoC user intends to use, so that it is
unnecessary to re-negotiate at a later time and set server-client media
parameters to be used in the future. In order to establish the early
session, the PoC client provides the media parameters supported to a
Session Description Protocol (SDP) body through an SIP INVITE method, and
makes a response to the media parameters provided from the server,
thereby returning, to the PoC user, identification information of the
early session which is newly set to the response message from the server
together with a conference URI (Uniform Resource Identifier). In the case
of making use of this early session, it is possible to previously set an
IP address, a port number, a talk burst control protocol for controlling
a codec, and a talk burst that are to be used, and so forth.

[0023] The on-demand session mode refers to a state where the PoC user
does not establish the early session, and means that the PoC user
receives an INVITE message of another PoC user to then perform a PoC call
connecting procedure.

[0024] Meanwhile, the PoC specification that is being standardized by the
OMA includes the following special features except the basic functions of
the communication system as mentioned above.

[0025] First, the PoC system supports a function of a Manual Answer
Override (hereinafter referred to as "MAO") which sends an auto-answer to
an authorized PoC user which is previously set by a PoC receiver (or a
reception side PoC user) regardless of the answer mode of the PoC
receiver and connects communication at a receiving terminal. A request of
the MAO is supported only to an authorized communication requester, and
is sent with an MAO indication included in a PoC communication request
message (or INVITE). This MAO request is devised for public services and
for emergency services (e.g., police, fire, accident, disaster relief,
other emergencies, etc.)

[0026] Moreover, the PoC system allows both the PoC server as an element
on a network and the PoC client as a terminal of the user side, to set
the answer mode to the communication request.

[0027] When being set in the network, the answer mode is implemented at
the PoC server that performs the PF within a home network to which the
PoC client belongs. In this case, it is characterized in that the
communication requesting procedure can be simplified as compared with the
case wherein the answer mode of the PoC client is reflected on the PF
which is connected to the PoC client, and then an answer is made.

[0028] Finally, the PoC user can set the answer mode by using its own
client. At this time, it is characterized in that the answer mode of the
PoC user's own client has priority over the answer mode set on the
network. This is for solving a privacy problem which occurs when the PoC
user changes its own answer mode by using the terminal to request the PoC
server to update the answer mode, particularly when the answer mode is
not reflected in real time due to a signal delay or error in a radio
access network or an IP core network. In order to solve this privacy
problem, the PoC service can set the answer mode of the user for both the
PoC server and the PoC client, and the PoC server and the PoC client
perform operations as determined by the answer mode of the PoC client
which complies with a user's desires.

[0029] Depending upon various functions and features of the PoC system,
the call processing may be variously performed. Particularly, in the
present invention, when the pre-established session is provided on the
PoC call reception side and when the one-to-one communication of
requesting the MAO on the PoC transmission side is requested, the process
and or method for complying with the call request and performing the call
processing is performed.

[0030] In reality, requesting the MAO on the PoC transmission side is
usually occurs during emergency situations. In the process of actually
requesting the MAO on the PoC transmission side, unnecessary steps are
performed, which causes an unnecessary time delay. This unnecessary time
delay will now be discussed with reference to the transmission side and
to the reception side of conventional systems.

[0031] A flow chart illustrating a conventional process of setting a
reception side PoC communication for an MAO is shown in FIG. 2, and a
flow chart illustrating a conventional process of setting a transmission
side PoC communication for an MAO is shown in FIG. 3. As shown in FIGS. 2
and 3, call processing procedures of call transmission and reception
sides are illustrated for a conventional communication system in which a
PoC communication sender makes a request for call processing based on an
MAO indication and when an early session is established on the reception
side.

[0032] With reference to FIG. 2, a PoC client A sends an INVITE request to
a SIP/IP core A, wherein the INVITE request includes information on a SIP
address of a receiver which the PoC client A wants to invite (Step 101).

[0033] Here, the INVITE request includes an information element indicating
the MAO, and is sent to a Participating PoC server A via the
corresponding servers (P-CSCF (Proxy-Call Session Control Function) and
S-CSCF (Serving-Call Session Control Function)) within an IMS core
network by means of a query about a path in a DHCP (Dynamic Host
Configuration Protocol) server or a DNS (Domain Name System) server (Step
102).

[0034] On making a request for a general call, the Participating PoC
server connected with a PoC user may be separated from a Controlling PoC
server for managing a talk burst of an opened session. Hence, the INVITE
request sent in Steps 101 and 102 is sent to a Controlling PoC server X
via a SIP/IP core of each network (Steps 103 to 105).

[0035] The Controlling network including a CF (not shown) sends the INVITE
message sent in Step 105 to the corresponding SIP/IP core, and then
receives a response message. A SIP response message from the reception
side network may be a provisional response message, a successful response
message, or an error message. These messages each comprise a 3-digit
code. For example, the provisional response message comprises a 3-digit
code beginning with a 1 such as 1xx; the successful response message
comprises a 3-digit code beginning with a 2 such as 2xx; and the error
response messages comprise a 3-digit code beginning with a 4, a 5, or a 6
such as 4xx, 5xx and 6xx. These codes are described below with reference
to Table 3.

[0037] After Step 105, the CF of the controlling network may receive an
auto-answer or a manual answer, particularly an OK response.
Alternatively, in the case of the auto-answer as in FIG. 2, a 183 Session
Progress signal (the provisional response signal) (not shown) may be
received, and thereby a connection between the PoC server and the PoC
client may be performed in the IMS network of the communication
requester. A communication permission signal of the receiver responds
with the final OK response, and is sent to the PoC client A via the CF
and the PF of the PoC server (Steps 106 to 110). Meanwhile, the CF
receives an OK response signal of the receiving client, and then
determines that a PoC communication is connected. As a result, the CF
sends a Floor granted signal that assigns a talk burst floor to the PoC
client A.

[0038] The PoC client A receives the OK response and Floor granted signals
with respect to the INVITE request signal, and then sends a Send talk
burst signal first by using a RTCP (Real-time Transport Control
Protocol), wherein the Send Talk Burst signal indicates that a user of
the PoC client sends the talk burst prior to making the user hear a ring
back tone. Here, the Send Talk Burst signal includes information
including a PoC address, a display name etc., of the transmission side
PoC client. Because the Send Talk Burst signal makes use of a path of a
media bearer, it can be sent without passing through the SIP/IP core
network.

[0039] After sending the Send talk burst signal, the PoC client informs
the user of the communication connection and sends media (typically, a
voice) of the user by using the RTP.

[0040] FIG. 3 is a flow diagram illustrating a reception side call
processing procedure according to the prior art when an early session is
established which corresponds to a transmission side communicating
procedure and an MAO request is sent.

[0041] A procedure where the INVITE message including the MAO request is
sent to the PoC server belonging to a home network of the reception side
PoC client via the SIP/IP core according to the call processing procedure
of the IMS network is shown in Steps 201, 202 and 203.

[0042] At this time, a Participating PoC server B may have a setting value
of its own answer mode, i.e., has a parameter of any one of its own auto-
and manual-answer modes. However, the Participating PoC server B checks
an MAO indication in the INVITE request message, and then sends an
auto-answer message to the call request network (Steps 204, 205 and 206).

[0043] In general, this auto-answer message is the SIP message called the
"183 Session Progress" as mentioned above, which is sent to a Controlling
network. The Participating PoC server B sends an INVITE or re-INVITE
request message to the PoC client having the corresponding PoC address
which was sent in Steps 204, 205 and 206 (Steps 207 and 208). Steps 207
and 208 serve to inform the PoC client that a PoC call request of making
a request for the MAO is received. The PoC client B then automatically
sends an OK response without confirmation by the PoC user (Steps 209 and
210).

[0044] The Participating PoC server B receiving the corresponding OK
response sends a response message responding to the MAO INVITE to the
transmission side network to complete the PoC call processing procedure
(Steps 211 to 215). The PoC Server X sends a Receiving talk burst signal
to PoC Server B (Step 217). The PoC server B then sends the Receiving
talk burst signal to the PoC client B, wherein the Receiving talk burst
signal includes the PoC address and display name of a person who makes
the PoC communication before the PoC client sends the media (Step 217).

[0045] Finally, the media (voice) sent on the transmission side is sent to
the PoC client B by using the RTCP by means of the connected media
bearer, so that the communication is initiated.

[0046] FIG. 4 is a table which illustrates information included in an
INVITE request of a PoC call.

[0047] It can be seen that information elements included in the INVITE
message requested on the transmission side include (1) PoC addresses of
PoC call requester, (2) media parameter information presented at the
client and server, (3) an indication informing a PoC service, (4) PoC
addresses of PoC call receiver, (5) an indication set at the PoC server,
(6) a talk burst control protocol to be negotiated with each other at
both ends of the transceiving network and so forth, and (7) alternatively
an MAO (Manual Answer Override) indication.

[0048] The procedure of processing the MAO communication request with
respect to the client having the early session as set forth in the prior
art includes the procedure of checking the MAO request indication at the
PF to send the auto-answer, but it does not have a great influence on the
final PoC communication connection between the transmission side network
and client. In the procedure of processing the MAO communication request,
after the OK response message received from the client arrives at the CF
and the transmission side network, both connection of the media bearer
and transmission of the Floor granted signal for making the actual PoC
communication are performed.

[0049] However, the communication request message including the MAO is
characterized in that it can be processed regardless of the answer mode
of the reception side user, and has a function of sending the talk burst
transport message by using the RTCP packet so as to display the PoC
address information and display name before the media is sent to the
reception side client. For this reason, the conventional procedure as
shown in FIG. 2 cannot be referred to as an optimized procedure of the
MAO call processing due to repetitive request-response signaling. In
particular, for emergency and public use purposes, quick call processing
is desirable.

SUMMARY OF THE INVENTION

[0050] Therefore, it is an object of the present invention to provide a
call processing system and method based on an answer mode of a PoC user
capable of simplifying a process of executing an MAO in order to
accommodate situations when there is no time to lose, such as during
emergencies. The call processing system and method of the present
invention is based on an IP Multimedia Subsystem (IMS) network which is
desirable for connecting a communication of a half duplex-type
communication and a communication of the PoC system which enables instant
communication according to a communication request by using presence
information of a user.

[0051] In order to accomplish this objective, according to one aspect of
the present invention, there is provided a call processing system based
on a manual answer override (MAO) in a Push-to-Talk over Cellular (PoC)
network. The call processing system includes a transmission side PoC
system having a transmission side PoC client and a transmission side PoC
server for sending a PoC communication request message to a reception
side PoC server, the PoC communication request message including an MAO
indication, and a reception side PoC system having the reception side PoC
server for recognizing the MAO indication included in the PoC
communication request message received from the transmission PoC server
and sending a response message to the transmission PoC system in response
to the PoC communication request message, and a reception side PoC client
for receiving a talk burst signal including the MAO indication from the
reception side PoC server.

[0052] According to another aspect of the present invention, there is
provided a call processing method based on a manual answer override (MAO)
in a Push-to-Talk over Cellular (PoC) network. The call processing method
includes the steps of sending a PoC communication request message
including an MAO indication from a transmission side PoC server to a
reception side PoC server; recognizing, by the reception side PoC server,
the MAO indication included in the PoC communication request message and
sending a response message to the transmission PoC server in response to
the PoC communication request message; and receiving, by a reception side
PoC client, a talk burst signal including the MAO indication from the
reception side PoC server.

[0053] According to yet another aspect of the present invention, there is
provided a method for performing a manual answer override (MAO) in a
Push-to-Talk over Cellular (PoC) network. The method includes the steps
of: receiving a talk burst signal including an MAO indication from a PoC
server; and detecting the MAO indication included in the talk burst
signal, the MAO indication being first MAO information sent from the PoC
server to a PoC client.

[0054] According to still another aspect of the present invention, there
is provided a Push-to-Talk over Cellular (PoC) client for performing a
manual answer override (MAO) in a PoC network. The PoC client receives a
talk burst signal including an MAO indication from a PoC server and
detects the MAO indication included in the talk burst signal, wherein the
MAO indication is the first MAO information sent from the PoC server to
the PoC client.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] A more complete appreciation of the invention, and many of the
attendant advantages thereof, will be readily apparent as the same
becomes better understood by reference to the following detailed
description when considered in conjunction with the accompanying
drawings, in which like reference symbols indicate the same or similar
components, wherein:

[0056] FIG. 1 is a block diagram illustrating a general PoC service
system;

[0057] FIG. 2 is a flow chart illustrating a conventional process of
setting a reception side PoC communication for an MAO;

[0058] FIG. 3 is a flow diagram illustrating a conventional process of
setting a transmission side PoC communication for an MAO;

[0059] FIG. 4 is a table which illustrates information included in an
INVITE for a request of a PoC call;

[0060] FIG. 5 is a flow diagram illustrating a process of setting improved
PoC communication for an MAO according to the present invention; and

[0061] FIG. 6 illustrates a payload format of a RTCP packet including an
MAO indication in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0062] Hereinafter, a push to talk over cellular user will be described
with reference to the accompanying drawings.

[0063] FIG. 5 is a flow diagram illustrating a process of setting improved
PoC (Push-To-Talk (PTT) over Cellular) communication for an MAO (Manual
Answer Override) according to the present invention. As shown in FIG. 5,
the circuit embodiment is directed to a procedure of processing an MAO
communication request with respect to a PoC client in which a
pre-established session exists, and shows a call processing procedure for
PoC communication which is proposed in an embodiment of the present
invention.

[0064] First, a Controlling PoC server receives an INVITE message
including an MAO indication from a network of a PoC communication
requester (or, a requesting PoC user) (Step 1000). Then, the INVITE
message is sent through an SIP/IP (Session Initiation Protocol/Internet
Protocol) core of a Controlling network and a SIP/IP core of a reception
side home network (Steps 1001, and 1002, respectively) to a Participating
PoC server belonging to the reception side home network of a PoC
communication receiver (or, a receiving PoC user) (Step 1003).

[0065] At this time, the Participating PoC server processes information
included in the INVITE message, such as a PoC address of the PoC
communication receiver, a PoC address of the PoC communication requester
and an MAO indication, and uses the processed information for the call
processing.

[0066] Meanwhile, the Participating PoC server can determine that a
session pre-established with the corresponding PoC user exists by using
the address information, and recognizes the MAO indication to send an OK
response signal in response to the INVITE request message regardless of
an answer of the PoC user which is forwarded to the Controlling PoC
Server via the SIP/IP of a reception side home network (Steps 1004 to
1006).

[0067] Then, the OK response signal returns to a route of the INVITE
request message according to a routing rule of an IMS (IP Multimedia
Subsystem) network.

[0068] The establishment of the auto-answer procedure of the steps 1004 to
1006 is possible because the Participating PoC server uses the
pre-established session's media parameters which the Participating PoC
server negotiates with the receiving PoC user in advance. Moreover,
because the information of the MAO indication is used to predict that the
PoC communication requester is an authorized user with respect to the
corresponding PoC communication receiver, the reception side PoC client
accepts the PoC communication request without reserve.

[0069] This predicted procedure is functionally compatible with
requirements defined in the current OMA standard and user cases, and
therefore there are no compatibility issues.

[0070] The above-mentioned OK response signal returns to the Controlling
PoC server of the Controlling network, and then is sent to the home
network of the PoC communication requester (Step 1007). At this time,
from the viewpoint of the transmission side of the PoC communication, the
OK response signal is recognized to be equal to what the receiving PoC
user directly permits the PoC communication and returns to the PoC
communication requester or the requesting PoC user. Thereby, a dialog is
established to complete a SIP based communication procedure.

[0071] Meanwhile, both the OK response signal and the Floor granted signal
are sent from the corresponding Controlling PoC server to the
transmission side PoC client (not shown) (Steps 1007 and 1008). The
transmission side PoC client then sends a talk burst transmission signal
including a PoC address and a display name thereof and the MAO indication
to a RTCP route (Step 1009). Finally, the Controlling PoC server of the
Controlling network sends a talk burst transmission signal including the
MAO indication to the reception side PoC client via the reception side
PoC server (Steps 1010 and 1011). At this time, the reception side PoC
user recognizes that the user granted the MAO by the reception side PoC
user requests the PoC communication (at this time, the name, the PoC
address etc. of the communication requester may be displayed), and
receives the media (voice signal) that is sent immediately.

[0072] FIG. 6 illustrates a payload format of a RTCP packet including an
MAO indication in accordance with the present invention. A configuration
of a RTCP packet that the transmission side PoC client sends may be
implemented in a payload format of the RTCP packet. The payload of the
RTCP packet includes general transmission-related information such as
version information, subtype information, length, etc. and MAO indication
information inclusive of the PoC address and name of the PoC user.

[0073] It should be noted that, in another embodiment of the present
invention, a step of including the MAO indication may be performed by the
transmission side PoC client belonging to the user terminal as mentioned
above, but the MAO indication can be performed by the Controlling PoC
server of the Controlling network or the receiving PoC server of the
reception side home network.

[0074] Meanwhile, according to use of the pre-established session, a route
between the PoC server and client and additional resource reservation may
be included. However, because the route and the resource reservation
depart from the gist of the present invention, they will not be described
herein. The requirements for the pre-established session which are
requested in the present invention do not influence the pre-established
session, but they can be more easily realized according to the expanded
definition of the pre-established session.

[0075] As set forth above, the PoC system provides various functions and
features, for example various PoC call processing procedures. In
particular, when the early session is established on the reception side
for the PoC communication and when the one-to-one communication of asking
for the MAO is requested on the transmission side for the PoC
communication, the request for communication is accepted to perform the
PoC call processing. The present invention proposes the PoC call
processing procedure and method which constitutes an improvement upon the
conventional procedure and method.

[0076] In general, the request for MAO is used for emergency
communications, public services and so forth. As such, the MAO request is
a service which requires the fastest procedure for PoC call processing.

[0077] According to the present invention, with regard to this MAO
request, a simple data field is added by using the RTCP, thereby
guaranteeing relatively fast communication processing. As a result, an
improved service can be provided in the aspect of the PoC user, and a
communication resource can be efficiently managed by reduction of
additional signaling in the aspect of the service provider. In
particular, because an answer mode is not synchronized between the PoC
user terminal and the PoC server, a fast communication processing method
can be implemented regardless of the generated race condition (where a
race condition is defined as an inconsistency between an answer mode
status set in a PF and a terminating PoC client.

[0078] While the present invention has been described with reference to
exemplary embodiments thereof, it will be understood by those skilled in
the art that various changes in form and detail may be made therein
without departing from the spirit and scope of the present invention as
defined by the following claims.